1. Field of the Invention
The invention relates to the inhibition of the formation of deposits inhibiting the flow of fluid in conduits and the like and, more specifically, to methods and devices for inhibiting the formation of unwanted deposits in downhole production equipment.
2. Description of Related Art
The problem of unwanted solid deposition in oil wells, gas wells, surface production equipment, and in hydrocarbon flow lines has presented a challenge to the petroleum industry since the first wells were drilled more than one hundred years ago. Although scale deposition is a major problem that interferes with the production of oil and gas, it is not the only problem. Paraffin or wax deposition has also been recognized as a major problem from the inception of the oil industry all over the world, as has asphaltene formation. The occurrence of these unwanted deposits in hydrocarbon producing conduits and related equipment can result in numerous problems, including reduced production and severe and often costly start up problems following pipeline shut down. Other problems with unwanted deposits can include congealing hydrocarbons, interface problems, depositions in tank bottoms, high line pressures, plugged flow lines, under deposit corrosion, plugging of injection wells and filter plugging.
Scale deposit and accumulation is a significant problem to oil and gas producer wells. The rate at which scale accumulates is dependent upon a variety of factors, including the quantity of minerals transported in the fluid, the temperature variations in the well bore, and pressure variations in the tubing, including variations resulting from tubing interior diameter changes. Once scale crystals begin to precipitate out of the fluid and form on the interior of the production conduit, the growth rate can accelerate. This phenomenon has been described as crystalline growth theory.
Chemical treatment methods for the removal of unwanted deposits such as scale, paraffin, asphaltene and hydrates, include acid treatments or the use of a variety of other chemicals to remove the unwanted deposits. Often, the type of chemical treatment method selected will vary depending upon the type of condensate or deposit. Chemicals, such as polyelectrolytes, phosphonates (such as DETPMP), polyphosphinocarboxylic acids (PPCA), organophosphonic acids (such as diethylenetriamine penta(methylphosphonic acid) and hexamethylenediamine tetramethylene phosphonic acid (HMDP)), and polymers such as polyacrylate (PAA), polyvinyl sulphonate (PVS), sulfonated polyacrylates, phosphomethylated polyamines (PMPA), and the ACUMER™ polymer products, such as ACUMER™ 2100, a carboxylate/sulfonate copolymer commercially available from Rohm and Haas Company (Philadelphia, Pa.) are often used to inhibit or prevent the growth of unwanted hydrocarbon deposits, such as scale crystals, on production tubing interiors. Other chemical-related treatments include the use of bacteria, enzymes, and continuous or batch down hole chemical injection and squeeze treatments of crystal modifiers. Typically, such chemicals are effective towards and limited to only specific types of deposits.
Despite their advantages, chemical treatments are usually expensive, environmentally hazardous in many cases, and are oftentimes very sensitive, working effectively only on specific crudes or on specific types of unwanted deposits. Chemical treatment often requires dedicated equipment to introduce the chemicals to the deepest sections of the well bore. Traditionally, scale prevention chemicals are injected down the annulus of the production tubing and enter the production tubing through sliding sleeves or other valves. In recent years, small stainless steel lines have been installed into the interior of the production tubing and run to the deepest point in the well bore. Scale prevention chemicals are pumped through the small line under pressure and mixed with the fluids produced from the well. This allows the fluid to be treated during normal production of the well, but requires continuous monitoring of the injection strings to maintain proper operation. In addition operation of the well is further complicated because access to the center of the production tubing is blocked, preventing through tubing, such as wire line or coiled tubing. Treatment chemicals are typically not recoverable from the production fluid.
Some deposits are so hard that chemicals are not effective, requiring physical methods for their removal, including mechanical removal. Physical methods have been studied and put to use for the past several decades as an alternative to chemical methods and to prevent and control unwanted deposit formation. Mechanical removal can include the use of drills, mills and other tools to grind or tear the deposits loose from the interior of the production tubing walls. Occasionally, such processes cause damage to the interior of the tubing and can cause worse scale accumulation rates in the future as a result. In worst-case scenarios, the production tubing must be extracted and replaced. Other physical methods which have been described include hot water circulation, steam injection, cutting or wire-lining, and the use of magnetic devices on electromagnets, such as solenoids and yoke-based electromagnets. However, while electromagnets can produce magnetic fields of great intensity, their choice for use in downhole environments is often not practical, as electromagnets need an electrical power supply, cooling, and require periodic servicing.
In contrast to electromagnetic devices, permanent magnet devices do not require an electrical down supply and require little to no maintenance. Several attempts have been made to use permanent magnet devices to reduce downhole buildup. Examples of several of the attempts include U.S. Pat. No. 3,228,878 which issued to Moody on Jan. 11, 1966 and discloses the use of magnets to provide a magnetic field having two polar zones a short distance from each other. The field may be provided by one or more high strength permanent magnets located outside the flow passageway and each having its poles facing toward the passageway in a direction normal to its path of flow. The magnetically treated liquid may flow with a minimum of turbulence and free it from external magnetic influence for a distance within the flow passageway from 10 to 150 times the length of the magnetic field to avoid too rapid a dissipation of the change effected therein by the passage through the magnetic field.
Another contribution to the art was made by Debney, et al. in U.S. Pat. No. 4,422,934, wherein a magnetic device for the treatment of calcerous fluids was disclosed. Described therein is a device for magnetically treating liquids to inhibit the deposit of scale in plumbing systems, appliances, boilers, and the like. The device has an elongate housing with an inlet and an outlet for the flow of liquid therethrough. A support structure is located inside the housing to retain a plurality of longitudinally spaced-apart magnets. The magnets are held in position by a plurality of transverse holding elements which are positioned so that the magnets are angularly disposed in a helical arrangement. The magnets are directly immersed in the liquid flowing through the device.
As a further example, U.S. Pat. No. 5,178,757 to Mag-Well, Inc. describes a device that includes an elongated hollow core providing at least one passage through which the fluid to be treated flows. An array of magnets extends longitudinally along the core with the poles of the magnets arranged so as to provide a magnetic field perpendicular to the flow path to enhance the magnetic conditioning effect of the tool. An alternative embodiment of the device has three longitudinally extending arrays of magnets with two fluid passages between them. The magnets are formed of a rare earth magnetic material, and are backed by a flux-carrying member of cobalt-iron alloy, with rounded corners so as to reduce loss of a magnetic field. Each magnet is mounted at least partially within an outer surface of the core with the flux-carrying member contacting, covering, and extending between the outer major faces of the magnets.
U.S. Pat. No. 5,052,491 issued to Harms, et al. on Oct. 1, 1991 describes the use of coupling devices that contain magnets to control the accumulation of paraffin and deposits in a downhole oil string or oil transmission flow lines. The coupling devices are made of a nonmagnetic material surrounded by a magnet and shield of magnetic material. The devices are used to join sections of oil string pipe together which form the downhole oil string casing. The magnetic coupling devices are placed at every 1,000 to 1,500 feet.
U.S. Pat. No. 5,453,188 issued to Florescu, et al. on Sep. 26, 1995 suggests an apparatus and method for preventing and minimizing the formation of deposits of paraffin, asphaltene and scale on the inside of downhole oil string line and on the surface of flow transmission lines. Successive magnet pairs are provided in magnetic discs along a section of pipeline. Each successive pair of magnets is rotated through a particular angle relative to the adjacent pair of magnets to achieve an advantageously prolonged trajectory of charged particles that populate the flowing fluid.
U.S. Pat. No. 5,700,376 issued to Carpenter on Dec. 23, 1997 describes an apparatus and method including first and second housing halves which are welded together to attach the apparatus to a pup joint installed in an oil casing. The housing includes a cylindrical portion and first and second frustoconical portions at opposite axial ends thereof. Axially extending L-shaped spacers are secured to the inside portion and include longitudinal edges which abut with the outer surface of the pipe. Series of axially spaced, first and right parallelepiped shaped magnets are sandwiched between the inside portion of the cylindrical portion and the outer surface of the pipe, with the poles of the first and magnets being reversed relative to the pipe. The housing halves are welded along their longitudinal free edges after being clamped together by a clamping band with sufficient force to secure the apparatus to the pipe generally by frictional forces and being free of the attachment to the pipe, and are secured along the casing pipe at approximately 1,000-foot intervals.
A Federal Technology Alert produced for the U.S. Dept. of Energy by Battelle Columbus Operations in January 1998 discloses the use of magnetic or electromagnetic scale control on a pipe through which water is flowing. It also discloses that manufacturers have applied the technology to petroleum pipelines to prevent wax build-up. A variety of other studies regarding the use and mechanisms of the use of magnets in treating scale, paraffin and asphaltene during petroleum production, including those by Farshad, F. F. et al. [SPE paper No. 77850, 2002; and, SPE paper No. 76767, 2002], and Tung, N. P., et al. [SPE paper No. 68749, 2001].
Applicants have created improved devices and methods for inhibiting deposit buildup in downhole hydrocarbon producing equipment.